One of the most active and challenging fields in molecular biology today is the genetic study of eukaryotic systems. An essential, but often rate limiting step in this area is the screening f DNA libraries for gene isolation. This procedure uses radiolabel hybridization techniques and autoradiography to achieve the required sensitivity and specificity. The particular part of the process that this proposal addresses is the measurement of the distribution of radioactivity on the transfer membrane which is normally measured with a 16 to 24 hour autoradiograph. We propose to utilize a new nuclear detector to generate a real time image of this distribution of radioactivity and to project this image directly onto the primary agar plate. In Phase I, we constructed a preliminary system and tested it with biological samples and demonstrated that the idea was feasible and that a useful image could be generated in less than 30 minutes. Using this new approach, not only will the researcher be able to harvest the appropriate plaques from the plate without the need to suffer the delays associated with autoradiography, but will also be able to carry out the procedure with a much higher level of confidence. Such an ability should significantly improve the efficiency of the entire procedure and allow more resources to be directed toward the analytical aspects of the work. The proposed detection system will allow researchers to obtain images of radioactive DNA libraries in real time which should significantly increase the efficiency of identifying and isolating pure DNA clones. The instrument, which will be relatively inexpensive, should find a strong commercial market in every recombinant DNA laboratory and molecular biology facility.